This application is based on Japanese Patent Application No. 11-275706 filed Sep. 29, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a piston for a swash plate type compressor, and more particularly to such a piston whose head portion slidably fitted in an appropriate cylinder bore is hollow and cylindrical.
2. Discussion of the Related Art
Since such a piston used for a compressor is reciprocated within a cylinder bore, it is desirable to reduce the weight of the piston. In particular, the reduction of the weight of the piston is desirable when the piston is used for a swash plate type compressor, especially where the swash plate type compressor is of a variable capacity type. As the swash plate type compressor adapted to compress a refrigerant gas for an air conditioning system of an automotive vehicle, there has been recently used the variable capacity type swash plate compressor whose discharge capacity is adjustable by controlling an angle of inclination of the swash plate with respect to its rotation axis. When the piston is used for this type of compressor, it is particularly required to reduce its weight. The swash plate type compressor for the automotive vehicle is generally required to be rotated at a high speed for satisfying a need for reduction of its size. In view of this, it is required to reduce the weight of the piston. Where the variable capacity type swash plate compressor is adapted to adjust the inclination angle of the swash plate based on a difference between a pressure in a pressurizing chamber and a pressure in a crank chamber, the reduction of the weight of the piston is essential for achieving a stable adjustment of the inclination angle of the swash plate and reduction of the operating noise of the compressor.
JP-A-10-159725 discloses a swash plate type compressor piston having a hollow cylindrical head portion. In the piston disclosed in this publication, a hollow cylindrical member is closed at its open end by a closure member, so at to provide the hollow cylindrical head portion. The piston thus produced has a reduced weight. The hollow cylindrical member and the closure member of this piston are both formed of an aluminum material.
It is an object of the present invention to provide a swash plate type compressor piston having an improved structure for a further reduction of its weight.
The object indicated above may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depend from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.
(1) A piston for a swash plate type compressor including a hollow cylindrical head portion and an engaging portion which engages a swash plate through a pair of shoes such that the shoes are held in contact with opposite surfaces of the swash plate at a radially outer portion of the swash plate, wherein the engaging portion is formed of a material which is different from that of an end section of the hollow cylindrical head portion, which end section is located on the side remote from the engaging portion.
Since the shoes are slidably received in part-spherical recesses formed in the engaging portion, the engaging portion is required to exhibit a sufficiently high degree of wear resistance, whereas the end section of the hollow cylindrical head portion, which end section is opposite to the engaging portion and partially defines a pressurizing chamber of the compressor, is required to exhibit a sufficiently high degree of strength rather than a high degree of wear-resistance. In other words, the engaging portion is required to be formed of a relatively expensive material to achieve the required wear resistance, while the end section of the head portion can be formed of a relatively inexpensive material. By using different materials for the engaging portion and the end section of the head portion, the piston can be produced at a reduced cost. In general, the outer circumferential surface of the head portion is coated with a wear-resistant synthetic resin film. In this case, the cylindrical wall of the head portion need not be formed of an expensive wear-resistant material, resulting in a further reduced cost of manufacture of the piston. An aluminum alloy containing not smaller than 5 wt. % of silicon is known as a wear-resistant material. This aluminum alloy is more difficult to be forged than an aluminum alloy whose silicon content is smaller than 5 wt. %. In view of this, if only a portion of the piston which constitutes the engaging portion which is required to have a high degree of wear resistance is formed of the wear-resistant aluminum alloy whose silicon content is relatively large, the other portion of the piston can be easily formed by forging, using the aluminum alloy whose silicon content is relatively small. Accordingly, the cost of manufacture of the piston is reduced.
(2) A piston for a swash plate type compressor having a swash plate, including a hollow cylindrical head portion and an engaging portion which engages the swash plate through a pair of shoes such that the shoes are held in contact with opposite surfaces of the swash plate at a radially outer portion of the swash plate, wherein the hollow cylindrical head portion includes a hollow cylindrical body portion having an open end on the side remote from the engaging portion and a closed end on the side of the engaging portion, the engaging portion and the hollow cylindrical body portion being formed, integrally with each other, of an aluminum alloy which contains not smaller than 5 wt. % of silicon, the hollow cylindrical head portion having a closure member which closes the open end of the hollow cylindrical body portion and which is formed of a material different from that of the engaging portion and the hollow cylindrical body portion.
The present arrangement permits easy manufacture of the piston having a lightweight, hollow head portion. The aluminum alloy containing not smaller than 5 wt. % of silicon exhibits an excellent wear resistance, so that the piston exhibits a required durability at its engaging portion. In other words, the engaging portion of the piston has excellent durability at part-spherical inner surfaces of recesses formed therein for slidably receiving the pair of shoes.
(3) A piston according to the above mode (2), the closure member is formed of a synthetic resin.
The closure member formed of a synthetic resin has a reduced weight, and can be economically manufactured by injection molding, for thereby reducing the weight and cost of manufacture of the piston. The synthetic resin preferably contains a glass fiber as a reinforcing material. The body portion formed of the aluminum alloy, and the closure member formed of the synthetic resin are fixed together by caulking the cylindrical body portion against the closure member, or by bonding the body portion and the closure member together. The body portion and the closure member can be firmly fixed together by employing these methods in combination.
(4) A piston according to the above mode (3), the hollow cylindrical body portion includes, on the side of the open end, an axial end portion which has an outside diameter smaller than that of the other portion of the body portion, the axial end portion being expanded radially outwardly by radial thermal expansion of the closure member formed of the synthetic resin at an operating temperature of the piston, so that the outside diameter of the axial end portion of the hollow cylindrical body portion is made equal to that of the other portion of the hollow cylindrical body portion during operation of the piston.
(5) A piston according to the above mode (2), the closure member is formed of an aluminum alloy which contains less than 5 wt. % of silicon.
Since an aluminum alloy containing less than 5 wt. % of silicon is suitable for manufacture by a forging operation, the closure member can be easily produced by forging. In the present arrangement wherein the hollow cylindrical body portion and the closure member are formed of the respective aluminum alloys whose silicon contents are different from each other, the body portion and the closure member can be firmly fixed together by press-fitting the closure member at its outer circumferential surface into the inner circumferential surface of the hollow cylindrical body portion, or by welding the body portion and the closure member together. A suitable adhesive agent may be used in combination with the above methods for fixing the body member and the closure member together.
(6) A piston according to the above mode (2), the closure member is formed of a material which contains magnesium as a major component.
The material whose major component is magnesium has a low specific gravity, so that the weight of the closure member can be easily reduced, resulting in reduction of the weight of the piston. In the present arrangement wherein the hollow cylindrical body portion and the closure member are formed of the respective different metallic materials, the body portion and the closure member can be firmly fixed together by press-fitting the closure member at its outer circumferential surface into the inner circumferential surface of the body portion, or by welding the body portion and the closure member together. A suitable adhesive agent may be used in combination with the above methods for fixing the body portion and the closure member together.
(7) A piston according to any one of the above modes (2)-(6), the aluminum alloy contains less than 13 wt. % of silicon.
The aluminum alloy whose silicon content exceeds 13 wt. % contains silicon in the form of primary crystal, making it difficult to form the components of the piston by forging. On the other hand, the aluminum alloy whose silicon content is not larger than 13 wt. % contains silicon in the form of eutectic silicon, so that the engaging portion and the hollow cylindrical body portion can be formed integrally with each other by forging, resulting in a reduced cost of manufacture of the pistion.
(8) A piston for a swash plate type compressor having a swash plate, including a hollow cylindrical head portion and an engaging portion which engages a swash plate through a pair of shoes such that the shoes are held in contact with opposite surfaces of the swash plate at a radially outer portion of the swash plate, wherein the hollow cylindrical head portion includes a hollow cylindrical body portion which has an open end on the side of the engaging portion and a closed end on the side remote from the engaging portion, the hollow cylindrical body portion being formed of an aluminum alloy containing less 5 wt. % of silicon, the hollow cylindrical head portion having a closure member which closes the open end of the hollow cylindrical body portion, the closure member being formed, integrally with the engaging portion, of an aluminum alloy containing silicon in an amount of 6xcx9c13 wt. %.
The aluminum alloy containing not smaller than 5 wt. % of silicon exhibits an excellent wear resistance, so that the piston exhibits a required durability at its engaging portion. In other words, the engaging portion of the piston has excellent durability at part-spherical inner surfaces of recesses formed therein for slidably receiving the pair of shoes. The aluminum alloy whose silicon content is not larger than 13 wt. % is more suitable for manufacture by a forging operation than an aluminum alloy whose silicon content exceeds 13 wt. %, so that the closure member and the engaging portion can be formed integrally with each other by forging. The aluminum alloy whose silicon content is less than 5 wt. % is particularly suitably used for manufacture by forging. Accordingly, the hollow cylindrical body portion which requires a large amount of stock removal from a blank in the form of the aluminum alloy can be manufactured by forging, permitting an economical manufacture of the piston having a reduced weight and improved durability. If the silicon content in the aluminum alloy is less than 3 wt. % or less than 1 wt. %, the body portion can be further easily manufactured by forging. Since the closure member which is formed integrally with the engaging portion, and the hollow cylindrical body portion are both formed of the aluminum alloys having respective different silicon contents, the body portion and the closure member can be easily welded together. The body portion and the closure member may be fixed together by press-fitting the closure member at its outer circumferential surface into the inner circumferential surface of the body portion. Further, a suitable adhesive agent may be used in combination with the above methods for fixing the body portion and the closure member together.
(9) A piston for a swash plate type compressor having a swash plate, including a hollow cylindrical head portion and an engaging portion which engages a swash plate through a pair of shoes such that the shoes are held in contact with opposite surfaces of the swash plate at a radially outer portion of the swash plate, wherein the hollow cylindrical head portion includes a hollow cylindrical body portion which has an open end on the side of the engaging portion and a closed end on the side remote from the engaging portion, the hollow cylindrical body portion being formed of a material containing magnesium as a major component, the hollow cylindrical head portion having a closure member which closes the open end of the hollow cylindrical body portion and which is formed, integrally with the engaging portion, of an aluminum alloy containing silicon in an amount of 5xcx9c13 wt. %.
In the piston according to the present arrangement, the closure member can be formed integrally with the engaging portion by forging, as in the piston according to the above mode (8). Although the body portion formed of the material whose major component is magnesium is not wear-resistant, the body portion has a reduced weight, and is welded to the closure member formed of the aluminum alloy. Alternatively, the body member and the closure member can be fixed together by press-fitting the closure member at its outer circumferential surface into the inner circumferential surface of the body portion. Further, a suitable adhesive agent may be used for fixing the body portion and the closure member together.
(10) A piston for a swash plate type compressor having a swash plate, including a hollow cylindrical head portion and an engaging portion which engages a swash plate through a pair of shoes such that the shoes are held in contact with opposite surfaces of the swash plate at a radially outer portion of the swash plate, wherein the hollow cylindrical head portion includes a hollow cylindrical body portion which has an open end on the side of the engaging portion and a closed end on the side remote from the engaging portion, the hollow cylindrical body portion being formed of a synthetic resin, the hollow cylindrical head portion having a closure member which closes the open end of the hollow cylindrical body portion and which is formed, integrally with the engaging portion, of an aluminum alloy containing silicon in an amount of 5xcx9c13 wt. %, for thereby providing the hollow cylindrical head portion of the piston.
If the synthetic resin is used for forming the hollow cylindrical body portion, the body portion has a reduced weight and can be economically manufactured by injection molding, resulting in reduction of the weight and cost of manufacture of the piston. The synthetic resin preferably contains a glass fiber as a reinforcing material.